This invention relates to optically isotropic devices or components, and more particularly to optically isotropic devices or components made of an optically isotropic polymeric material which is a blend of at least two completely miscible polymers.
By the term "optically isotropic", it is intended to refer to the properties in certain materials that their optical properties are the same in all directions. Optically, such properties include the index of refraction and light absorption. Very few materials are optically isotropic. Few, if any molded organic polymeric materials are optically isotropic. Such transparent or partially transparent polymers as polyethylene, Lucite (trademark of the duPont Company), polymethylmethacrylate (PMMA), etc., are not, strictly speaking, optically isotropic. This may be seen by making a relatively thin layered sample of the polymeric material and then determine its birefringence and absorption of polarized light. Birefringence of the sample is determined by finding the indices of refraction of the sample for polarized light in one direction and that for polarized light in a direction perpendicular to the first direction. The difference in the two indices of refraction is the birefringence of the sample material. In an optically isotropic material, birefringence should be zero. In measuring the light absorption of the sample, the two polarized lights are passed through the sample and the difference in the sample's absorption of the two polarized lights is a measure of the anisotropic nature of the sample material. Moreover, even when a polymeric material has zero birefringence in its bulk state, the processing of such a material into a device, such as by extrusion or injection molding, would place stress on the material in the direction of flow. Such mechanical stress would induce orientation of the polymer molecules which almost always results in induced birefringence.
In certain optical devices, such as optical disks used in the recording and the retrieving of information thereon, it is required that the materials forming various layers therein be optically isotropic. Accordingly, there is a need for optical devices or components of optical devices which are optically isotropic.
It is, therefore, an object of the present invention to provide optically isotropic device and components of such devices.
It is a further object of the present invention to provide optical devices and components of such devices which retain their optical isotropic characteristics even after mechanical stresses have been placed on the polymeric material to orient the molecules therein.
These and other objects of the invention will be apparent from the following detailed disclosure.